This invention relates to a seal construction and, more particularly, to a liquid chromatographic apparatus utilizing the seal construction.
In various analytical procedures, including liquid chromatography, a large number of liquid samples are processed sequentially in the same apparatus. In these processes, a conduit such as a hypodermic needle is immersed sequentially in a series of different samples which are interspersed with a cleansing solvent so that there is no cross sample contamination within the apparatus due to a portion of a sample processed in an earlier step being admixed with a subsequently processed sample.
As disclosed in U.S. Pat. Nos. 3,916,692; 4,094,195 and 4,094,196 sample injection means for liquid chromatographic apparatus are utilized which include a reciprocating sampling conduit in the form of a hypodermic needle. The needle is adapted to enter a series of sample containers sequentially so that the samples can be delivered to a downstream liquid chromatographic apparatus with a solvent under pressure. The flow of solvent is controlled so that it carries the sample to the liquid chromatographic apparatus and so that it cleans the liquid pathway so that subsequentially processed samples are not contaminated. In these chromatographic processes, liquids are processed at pressures up to 6,000 psig and even higher. Accordingly, when processing a sample, its flow must be confined, as much as possible, to the hypodermic needle carrying the sample and to the pathways leading to the downstream chromatographic apparatus. Accordingly, it is essential that suitable sealing means be included in the sample handling apparatus.
These seals are positioned concentric to the bore of the injection apparatus through which the sample passes by means of an hypodermic needle. The seals also are positioned above and below a hole in the needle which is the point of injection of the sample from the hypodermic needle into the high pressure solvent stream. By operating in this manner, the injected sample is contained by the seals thereby eliminating contamination of subsequently processed samples.
It has been proposed to utilize seals positioned concentric within the bore which seals comprise a jacket having a U-shaped cross section into which is positioned an energizing means such as a spiral wound spring, a U-shaped metal wedge or an O-ring made from an elastomeric material. These energizers tend to spread the walls of the U-shaped cross section so that the jacket walls bear upon the inner surface of the bore and on the outer surface of the hypodermic needle passing through the bore thereby to effect the seal. The spiral wound and U-shaped energizers are undesirable since they provide low values of a non-uniform pressure along the axial length and circumference of the jacket within which they fit so that there are areas of low pressure along the axial lenght of the jacket which may cause leakage. The O-ring energizers are undesirable since they are formed of elastomeric materials which are prone to lose sealing pressure as a result of creep with time or cyclical exposure to temperature.
Accordingly, it would be desirable to provide a sealing means capable of withstanding all the pressures encountered during liquid chromatographic processes and which provide uniform pressure along the axial length and circumference of the seal through which a hypodermic needle carrying a sample passes.